The present invention relates to an electro-hydraulic operating system for an extensible boom of a crane or the like. More specifically, the present invention relates to an improved valving system for enabling independent actuation and speed control of respective boom sections of a multi-stage boom.
Heretofore, operating systems of multi-stage booms for cranes, aerial work platforms or the like have taken various forms. In simplest form, the operating system may be primarily hydraulic with mechanical actuation controls. In more sophisticated forms, the operating system is electro-hydraulic, and the input control functions to the hydraulic cylinders are electrically generated by an operator from a control console in the cab of the crane. Whether the operating systems are primarily hydraulic or electro-hydraulic, some of the control functions of the boom of the crane are semi-automatic, and some are desirably completely automatic, not requiring any operator intervention.
Whatever type of operating system is employed for the multi-stage extensible boom of a crane or the like, operation of the system is extremely complex for an operator involving a great deal of training and skill. Accordingly, it is highly desirable to be able to automate the operation of extensible booms as much as possible in order to decrease the learning curve for operators, and also to implement automatic safety features. In order to accomplish this, some automated systems presently available utilize electronically programmable microprocessors to control the movement of the respective extensible sections of a multi-stage boom. Various features are programmed into the microprocessor, such as essential safety features relating to boom length; the relative location of boom sections for specific tasks; and the azimuth of the boom.
Conventionally, operators of cranes are provided with "load tables" for different optimum modes of operation. For example, a "load table" for optimum stability would be provided which specifies different extension lengths of respective boom sections, overall boom length and preferred sequences of movement of the respective boom sections to achieve the final section positions in the selected mode of operation. A similar type of table would be provided for optimum strength applications for the boom. Tables of this type are very complex and much training is required before an operator is facile with the various aspects. Accordingly, it is desirable to be able to program these tables into a microprocessor, so that these optimum modes of operation can be implemented automatically under control of the microprocessor with only minimal operator assistance.
Another important control function for extensible boom cranes is the speed of movement of the respective sections of the boom, not only during steady state movement within any movement cycle of a given section, but also at the beginning, or start, of movement and at the end, or stopping, of the movement of the section. Naturally, it is desirable to be able to automate controls of this type to avoid the need for operator control or assistance.
Accordingly, there is a need in the art for an improved electro-hydraulic valving system which is compatible with the needs of microprocessor controlled, multi-stage extensible booms for cranes or the like.